Plastic extrusion coater



Jan. 14, 1969 H. A. ARBIT 3,421,964

PLASTIC EXTRUSION COATER Filed Nov. 2v, 196s A TTORNE YS United States Patent Ofiice 3,421,964 Patented Jan. 14, 1969 3,421,964 PLASTIC EXTRUSION `COATER Harold A. Arbit, Rockford, Ill., assignor to Beloit Corporation, Beloit, Wis., a corporation of Wisconsin Filed Nov. 27, 1963, Ser. No. 326,628 U.S. Cl. 156-244 12 Claims Int. Cl. B29c 27/00; B32b 31 00 The invention relates to coating machines, and more particularly to machines for coating web material such as paper with a film of thermoplastic polymer and to the method of coating.

A film of normally solid synthetic linear polymer sharp melting point can be coated upon a sheet of supporting base such as paper by feeding the sheet of supporting base together with a sheet of normally solid molten synthetic linear polymer into the nip of two adjacent parallel rolls rotating in opposite directions, and cooling the roll which is in contact with the synthetic linear polymer while compressing the sheet of the supporting base material and the sheet of molten polymer between the said rolls thus producing a uniform coating of solid polymer on the paper or other base material. In accordance with the present invention a pressure differential is applied across the sheet at and/or slightly ahead of the nip flattening the sheet and drawing the film against the sheet.

It is an object of the present invention to improve the adhension of a plastic film coating to a web material joined in accordance with the above arrangement by bringing the coating and web material into more intimate better contact during the time they are joined in the nip.

A further object of the invention is to provide a method and apparatus for making an improved laminated product of a thermoplastic polymer film coated over a paper web wherein the surface fibers of the web are flattened prior to bonding with the film preventing the fibers from acting as wicks which adversely affects the permeability of the laminated sheet.

A further object of the invention is to provide an proved nip for joining a layer of molten film to a web of paper wherein the roll supporting the paper web is a suction roll.

Other objects, advantages and features will become more apparent with the disclosure of the preferred embodiment of the invention in the specification, claims and drawings, in which:

FIGURE 1 is a schematic elevational view of a plastic extrusion coater and constructed an operating in accordance with the principles of the present invention; and

FIGURE 2 is a fragmentary plan view of a suction roll which forms part of the laminating nip for the coater.

As shown on the drawings:

The mechanism for supplying the thermoplastic polymer film includes a hopper into which the normally solid thermoplastic is fed. The thermoplastic is heated such as by working and/or being heated by external heating means and is forwarded by an extruder 11. The material is delivered down through a die 12 in a thin sheet or film F such as polyethylene, which is received in a nip N between rolls 16 and 17.

The paper web W is received from a continuous supply fed over a pre-heat roll 13 and subsequently passes over a spreader roll 14 such as a Mt. Hope roll to remove wrinkles and thereafter passes over an upper guide roll 15. The Web then passes down into the nip N between the rolls 16 and 17.

The supporting roll engaging the paper web W is in the form of a perforate suction roll 16 with openings 16a, FIGURE 2. A suction gland 18 opposite the nip is preferably situated so that a pressure differential in the form of a suction is applied across the web W ahead of the nip and in the nip N.

This suction fiattens the paper web to the supporting suction roll 16 and lays down the surface fibers of the paper web on the upper exposed surface just prior to bonding with the polyethylene. These surface fibers if permitted to freely project upwardly act as wicks drawing the liquid film into the paper and reducing its thickness at the location of the projecting surface fibers. This usually results in a location of reduced thickness of film on the surface of the laminated web thereby increasing the permeability of the coated paper. By applying the suction these fibers are laid fiat to the outer surface avoiding the wick effect and resulting in a more impermeable, more uniform coated paper.

The coated paper web C follows around the roll 17 which is chilled, and up over a guide roll 20.

The invention is preferably used in forming a coated paper but other base web materials may be employed and any web material having porosity to be affected by the suction is useful in the practice of the invention, and such base materials may be employed including paper, cardboard, textiles, porous and nonwoven films, and woven materials. The unique effect of the laying down of the paper fibers on the outer exposed surface of the paper web is obtainable only however with the coating of a travelling paper web.

The roll 16 is preferably rubber surfaced and the suction openings 16a provided therein are sufficiently close together so that a mottled or marked effect will not be a result of passing the film and web through the nip. Rubber surfaces of synthetic or natural rubber may be used and preferred rubbers for this purpose are vulcanized natural rubber, vulcanized chloroprene rubber and good results are also obtained from other synthetic rubbers such as vulcanized butadiene-styrene polymers, vulcanized butadiene-acrylonitrile polymers, vulcanized chlorosulfonate solid ethylene polymer, neoprene, silicone and the like. The rubber also may be coated with a thin film or layer of polytctraliuoroethylene, at least at the edges of the web to avoid the film etxending over the edges of the paper web and adhering to the rubber roll. This polytetrauoroethylene, known by the trade name Teflon, may be attached to the rubber roll such as by a pressure sensitive adhesive or may be a sleeve fitted over the roll. The film may be of any suitable thickness but it is preferred that it be thin so that it does not interfere with the compressibility of the rubber on the roll 16. For example, a film of Teflon of 0.002"0.005 inch thick has been quite suitable employing a rubber covering for the roll 16 having a Shore durometer hardness of about 60'.

The roll 17 is suitably chilled such as by internally circulating cold water therethrough, and the cooling should be sufficient to drop the temperature of the film below the solidilication point of the thermoplastic polymer used. The film is molten at the time of contact with the sheet and preferably in the temperature range of C.- 350 C. The film is chilled on the roll 17 to a temperature 3 of C. to 120 C. Suitable means is provided to maintain the temperature of the roll 17 at the desired temperature in the range of 5 C. to 60 C.

The suction in the suction roll 16 is sufcient to draw the film into good contact and to flatten the fibers on the surface of the paper web and a suction in the range of 1.0 inch to 23.0 inches of mercury is desired.

The surface of the roll 16 is cooled to protect and maintain the resiliency of the rubber, such as by Contact with a cooled roll 19.

The film for coating may be a synthetic linear polymer having a sharp melting point, and suitable polymers include normally solid ethylene polymers, polyamide resins (e.g., polyhexamethyleneadipamide; polypentamethylenesebacamide; polypropylene; polyamide mixtures obtained by interpolymerizing a mixture of hexamethylene-diammonium adipate and hexamethylene-diammonium sebacate with caprolactam; and indeed any of the other synthetic linear polyamides disclosed in U.S. Patents 2,071,250, 2,071,253, 2,130,948 and 2,130,523), chlorinated normally solid ethylene polymers, especially those having from 20% to 40% by weight of chlorine normally solid ethylene/vinyl acetate interpolymers, polystyrene, hydrolyzed normally solid ethylene/vinyl acetate interpolymers, and the like. The preferred polymer employed in the practice of the invention is normally solid ethylene polymer.

Thus it will be seen that I have provided an improved mechanism and method for coating travelling webs such as paper webs which meet the objectives and advantages above set forth. In operation the paper web is supported on the suction roll and flattened thereto with the outer exposed fibers fiattened against the roll to present an essentially smooth surface for engaging the film, and maintenance of the suction on the back side of the web draws the film intimately to the web. The resultant product is more uniform and has a greater moisture impermeability with each layer of the laminated film being more uniform and the line of contact being more accurately planar although the bond and adhesion between the layers is improved.

The drawings and specification present a detailed disclosure of the preferred embodiments of the invention, and it is to be understood that the invention is not limited to the specific forms disclosed, but covers all modifications, changes and alternative constructions and methods falling within the scope of the principles taught by the invention.

I claim as my invention:

1. A coating mechanism comprising, means for extruding a molten film of normally solid thermoplastic polymer, means for contacting the molten film with a supporting base of porous web material, opposed means engaging opposing sides of the web at the same location for compressing the molten film against said web material, one of which is a cooled surface in contact with the film, the other being a surface in contact with the web material, and means for applying a pressure differential across said other surface for the web material for flattening said web material and holding the film against the web material.

2. A coating mechanism comprising, means for extruding a molten film of normally solid thermoplastic polymer, means for contacting the molten film with a supporting base of porous web material, surface means compressing the molten film against the web material, one of which is a cooled surface in contact with the film, the other being a gas permeable surface, said means engaging opposite sides of the film and web material at the same location, and means applying a suction within said gas permeable surface for fiattening the web material and holding the film against the web material.

3. A machine including parallel counter rotating rolls adapted to bond in the nip between the rolls a thin sheet of heated normally solid thermoplastic surfacing material to a surface of a continuous sheet of porous web like material carried by one of said rolls, said one roll being a suction roll.

4. A coating mechanism comprising means for extruding a molten film of normally solid thermoplastic polymer for applying to a porous web material, a pair of rolls forming a compressing nip therebetween pressing said film to said web material, means for applying a pressure differential for attening the fibers on the surface of the web material prior to engagement of the web by the film.

5. A coating mechanism comprising, means for extruding a molten film of normally solid thermoplastic polymer for applying to the surface of a porous web, first and second rolls forming a compressing nip therebetween pressing said film to said web, said first roll engaging said web material and being hollow with a perforate outer wall, and a suction means within said first -roll opposite the nip.

6. A coating mechanism comprising, means for extruding a molten film of normally solid thermoplastic polymer, a pair of rolls forming a compressing nip therebetween for pressing said film to a porous web, said one roll engaging said web and being perforate, means cooling the other roll to the temperature in the range of 5 C. to 60 C., and means applying a suction within the perforate roll in the range of 1 to 23 inches of mercury.

7. A process of applying a film of normally solid synthetic linear polymer of sharp melting point to a porous sheet which process comprises carrying out substantially simultaneously the steps of contacting a molten film of polymer with said sheet, pressing said molten film against said sheet, applying a pressure differential across said sheet holding the film against the sheet, and chilling the exposed surface of said molten film to a temperature below the solidifcation point of said film while said pressure differential is maintained.

8. A process of applying a film of normally solid synthetic linear polymer of sharp melting point to a porous sheet which process comprises carrying out substantially simultaneously the steps of contacting a molten film of polymer with said sheet, pressing said molten film against said sheet, applying a suction to the back surface of said sheet, and chilling the exposed surface of said molten film while said suction is applied and cooling the film to a temperature below the solidifcation point of said film.

9. A process of applying a film of normally solid synthetic linear polymer of sharp melting point to a porous sheet which process comprises carrying out substantially simultaneously the steps of contacting a molten film of polymer with said sheet, said molten film at the time of contact with said sheet being at a temperature of C.- 350 C., pressing said molten film against said sheet, applying a pressure differential across said sheet holding the film against the sheet, and chilling the exposed surface of said molten film while said pressure differential is maintained across the sheet and cooling the film to a temperature in the range of 10 C.90 C.

10. A process of applying film of a normally solid synthetic linear polymer of sharp melting point to a porous sheet, which comprises feeding said sheet into the nip of two adjacent parallel rolls rotating in opposite directions, extruding a molten film of said polymer parallel to said rolls and downwardly into the nip of said rolls, applying a suction to the underside of said sheet at said nip, said film while in the molten state contacting said sheet at the nip of said rolls, and passing said film or sheet through the nip of said rolls under positive pressure from said rolls, said rolls in contact with said film being maintained at a temperature below the solidifcation point of said film.

11. A coating mechanism comprising means for extruding a molten film of normally solid thermoplastic polymer on a porous web material, means for applying a pressure dilerential for attening the fibers on the surface of the web material facing the molten lm prior to engagement of the web by the film, and a chill roll for engaging the molten lm on the web material While said fibers are held flat.

12. A coating mechanism comprising means for extruding a molten lm of normally solid thermoplastic polymer for engaging a continuous sheet of porous web material, means for applying a pressure dierential across the web material for flattening fibers on the Surface of the web material against the web material in advance of a chill roll which engages the -molten polymer on the web material While said pressure differential is being applied.

References Cited UNITED STATES PATENTS EARL M. BERGERT, Primary Examiner.

10 T. R. SAVOIE, Assistant Examiner.

U.S. C1. X.R. 

7. A PROCESS OF APPLYING A FILM OF NORMALLY SOLID SYNTHETIC LINEAR POLYMER OF SHARP MELTING POINT TO A POROUS SHEET WHICH PROCESS COMPRISES CARRYING OUT SUBSTANTIALLY SIMULTANEOUSLY THE STEPS OF CONTACTING A MOLTEN FILM OF POLYMER WITH SAID SHEET, PRESSING SAID MOLTEN FILM AGAINST SAID SHEET, APPLYING A PRESSURE DIFFERENTIAL ACROSS SAID SHEET HOLDING THE FILM AGAINST THE SHEET, AND CHILLING THE EXPOSED SURFACE OF SAID MOLTEN FILM TO A TEMPERATURE BELOW THE SOLIDIFICATION POINT OF SAID FILM WHILE SAID PRESSURE DIFFERENTIAL IS MAINTAINED. 